The present invention relates to an arc-image furnace for heating a sample such as many kinds of heat resistant materials etc. at elevated temperature and more particularly relates to a high pressure arc-image furnace for heating the sample optically at several hundreds to about 4000.degree.C and melting the same under a high pressure of 10 to several hundred atmospheres.
The heating apparatus of the present invention is characterized in that a heat source such as a lamp, an optical system and a sample to be heated are enclosed in a vessel which can withstand a high pressure of more than ten atmospheres, and the image of said lamp is projected to said sample through said optical system.
An arc-image furnace using a discharge lamp containing rare gas as a heat source thereof has hitherto been employed and is capable of being used continuously for several hundreds hours with a capacity of 30 KW because of development of the Xenon short-arc lamp of the cooled electrode type. Such arc lamp is expected to be used instead of the conventional carbonarc as a heat source of the furnace for heating heat resistant materials at several hundreds to about 4000.degree.C and melting the same.
However, almost all elements or compounds are evaporated rapidly, boiled or sublimated after they are melted at elevated temperature under subatmospheric or atmospheric pressure. Accordingly, there are not many applications of said arc-image furnace for heating such materials in spite of the fact that high temperature can be obtained by such furnace. Especially, there are few applications of the arc-image furnace in the case of more than 1,500.degree.C under atmospheric pressure or more than 2,000.degree.C under less than 10 atmospheres. It has hitherto been proposed that such furnace can be utilized with advantages for controlling the consistency of a small quantity of contamination of a semi-conductor etc. However, such furnace has not yet been used practically because of the evaporation, boiling, or sublimation of the sample or the contamination.
FIG. 1 shows a conventional heating apparatus. As shown in FIG. 1, in said heating apparatus a sample 1 and supporting means 2 for said sample 1 are enclosed in a vessel 3 containing gases of predetermined pressure and made of heat resistant transparent material such as transparent fused silica etc. A paraboloid mirror 7 for reflecting and concentrating short-arc 6 produced between electrodes 5, 5 is supported in the atmosphere. 9 designates an electric circuit for controlling arc current, 10 a gas source, 11 a valve of the gas source 10, 12 a manometer, 13 a transparent plate of silica, 14 a mirror, 15 a monitor such as an industrial television etc., and 25 a passage of high pressure gas.
In order to heat a sample under about 10 atmospheres by a lamp of a capacity of less than 30 KW, it is necessary to determine suitably the thickness of the wall and the inner diameter of said heat resistant transparent vessel 3 because the temperature and pressure at the inside of the vessel 3 are higher than that at the outside and there is a risk of explosion. The factor of safety of the vessel 3 under the static pressure is usually determined as 5. In order to use the vessel 3 under about 100 atmospheres with the factor of safety under the static pressure of 5, the thickness of the wall of vessel 3 must be determined as at least 40mm in case the inner diameter thereof is 80mm. In practice, the factor of safety becomes zero because of the vessel 3 being overheated partially by the high density light beam projected to the sample 1 positioned at the central portion of the vessel 3, the convection gas of high temperature emittted from the sample 1 heated at several thousands .degree.C and the thermal stress generated in the material of vessel 3 due to the large thickness thereof. Accordingly, the arc-image furnace as shown in FIG. 1 has not yet been used under a high pressure 10 to several hundred atmospheres.